短粗试样（矿柱）渐进破坏的围压效应

采用FLAC，在矿柱端面不存在水平摩擦力条件下，模拟了围压对矿柱渐进局部剪切破坏的影响。在弹性阶段，材料的本构关系为线弹性。峰值强度后的本构模型取为莫尔库仑剪破坏与拉破坏复合的应变软化模型。数值结果表明，随着围压的增加，矿柱的峰值强度、残余强度及应力降增加；剪切带图案变得不规则，对称性变差，发生塑性破坏的单元数量变少，被剪切带切割的块体尺寸及形状变得不规则；总软化区扩展率降低，因此，受到高围压作用的矿柱，不易发生失稳破坏。但在破坏前，前兆不明显；矿柱中部的均匀分布的水平及垂直应力增加，它们的分布具有某种相似性。在剪切带之外，垂直及水平应力均较高，这为剪切带沿其切线及法线扩展提供了所需要的、较高的应力梯度。应力分布的不均匀性，根源于矿柱发生了以多重剪切带为表现形式的局部剪切破坏。

Effect of Confining Pressure on Progressive Failure of Squat Specimen (Mine Pillar)

Characteristic of progressively localized shear failure of squat specimen(such as mine pillar)was modeled numerically by FLAC under the condition of smooth ends in horizontal direction.The failure criterion was a composite Mohr-Coulomb criterion with tension cut-off.Linear elastic and strain-softening post-peak constitutive relations were adopted.Increasing confining pressure acting on the two lateral edges of the pillar leads to(1)higher peak and residual strength as well as stress drop from the peak to the residual stage;(2)less regular and less symmetrical shear band patterns;(3)a decrease of the number of yielded elements;(4)smaller blocks(separated by shear bands)exhibiting different sizes and shapes;(5)a decrease of the ratio of the thickness of total softening zone surrounding the elastic core to the relative vertical displacement of the pillar and(6)higher horizontal and vertical stresses remaining uniform at the center of the pillar.The pillar subjected to higher confining pressure does not easily lose its stability;however,no obvious precursor to failure is observed prior to the occurrence of instability.Generally,the distributions of the horizontal and vertical stresses have similarity to some extent.Outside shear bands,the higher horizontal and vertical stresses reached contribute the further development of shear bands along their normal and tangential directions.Non-uniformity of the horizontal and vertical stresses stems from the localized failure in the pillar in the form of multiple shear bands.